The Animal Model Core will maintain breeding stock of C57/BL/6 and DBA/2 mice, of 22 BXD recombinant inbred (RI) strains derived initially from these strains, and of an F2 generation derived from the same strains. Mice will be produced from these stocks in sufficient number to meet the statistical requirements for cross-sectional biomarker assessment beginning at approximately 150, 450, or 750 days of age. An additional F2 group will be produced that will be maintained until natural death. All animals will be born, reared, and maintained in a specific-pathogen- free barrier facility. This Core will also serve as the common resource for the genotyping will also serve as the common resource for the genotyping of all of the subject animals for which genotyping is required, in order to provide the relevant data enabling the detection of quantitative trail loci (QTLs). The pathological analysis of all cross-sectional animals will also be the responsibility of this Core.